Variable frequency oscillator



March 31, 1953 F. B. ANDERSON VARIABLE FREQUENCY OSCILLATOR Filed Feb. 1. 1950 18 Sheets-Sheet 1 FIG! ourpur PHhsE 4 OUZPUFPHA$3 ourPur PHASE I) lNl/ENTOR I? 8. ANDERSON U0 W ATTORNEY March 31, 1953 F. B. ANDERSON 2,633,534

VARIABLE FREQUENCY OSCILLATOR Filed Feb. 1, 1950 l8 Sheets-Sheet 3 r r r c 2 0 2 c z' c 2 a c c 2 c z c 2 a e .i. CONSTANT CURRENT W\AMMN- BRIDGE ?k k (R (R ourPur e' e e I CONSTANT cums/w ay 5mm e li e- INVENTOR E B. ANDERSON ATTORNEY March'3l', 1953 F. B. ANDERSON VARIABLE FREQUENCY OSCILLATOR Filed Feb. 1, 1950 18 Sheets-Sheet 4 mam/r005 srr//vas NEAR HIGH AND "X-QQ% @J N,P LOW FREOUENCYBYTREMES ssrruva o 0 -9 -/ao PHASE ANGLE /N VE N 7' OR E B. ANDERSON A TTORNEV March 31, 1953 Filed Feb. 1, 1950 18 Sheets-Slieet 5 FIG. 7A

mam/runs JAX/s 2. wrmuzomrs 2 FRE UENCY 2 FREQUENCY 0 I f REAL AXIS I osc -a f I 05C PHASE ANGLE I I /30- f FREQUENCY use /a0" 2 I FIG. 7B

MAM/W305 LOW mguavcv 3- 27-. JAX/S SETTING I me'outzvcv (E LG 0 I I REAL AXIS T PHAsf-ANGLE l 'Ax/s 3. H161; g ggzlvcv F f T msous/vcv a 9 o f RE4L AXIS 3.21% a FIG. 8A

vr w R l I I Z 55 VT 7 s INVENTOR ATTORNEY March 31, 1953 F. B. ANDERSON 2,633,534

VARIABLE FREQUENCY OSCILLATOR Filed Feb. 1, 1950 18 Sheets-Sheet s 1:" a. ANDERSON ATTORNEY March 31, 1953 F. B. ANDERSON 2,633,534

VARIABLE FREQUENCY OSCILLATOR l8 Sheets-Sheet 7 Filed Feb. 1. 1950 INVENTOR F B. ANDERSON A r TOAWEY March 31, 1953 F. ANDERSON VARIABLE FREQUENCY OSCILLATOR Filed Feb. 1, 1950 18 Sheets-Sheet 8 FIG.

mm 0 m MM F w v. B 3 n C l \L c M. 0 /A n 3 f MP n g ATTORNEY March 31, 1953 F. a. ANDERSON 2,633,534

VARIABLE FREQUENCY OE CILLATOR Filed Feb. 1, 1950 18 Sheets-Sheet 10 FIG. /4A 1 A E- mit l p; PI

o 1r=a3 as 0.7 FIG/4B -arc mn[- 4(o.2/)] FOR A: 0.3, 0. 7 a.rc tan -4(o.25) FOR K=0.5 FIG. /5 T 01a,, l

i km AXIS //vv/vro/? F 8. ANDERSON ATTORMY F.'B.- ANDERSON VARIABLE FREQUENCY OSCILLATOR March 31, 1953 18 Sheets-Sheet 11 Filed Feb.' 1, '1950 F IG. /6A

FIG/7B FIG. I714 SCREEN GENEIMTORS FIG. /7C

m m 2 8% h m m w Q .Q 2 0 NW 2 z o m 2 MM 7. A 9 mm a a FC 1 Z/ 0 SCREEN DECOUPLl/VG IMPEDANCE S INVENTOR F B. ANDERSON BY ATTORNEY "Filed Feb. 1, 1950 March 31, 1953 F. B. ANDERSON 2,633,534v

VARIABLE FREQUENCY OSCILLATOR l8 Sheets-Sheet l2 LOG MAGN/TUDE 2,

RfR

F/azoo R f z PHASE ANGLE -9o-- 0H,

INVENTOR E B. ANDERSON A TTORNEV March 31, 1953 F. B. ANDERSON VARIABLE FREQUENCY OSCILLATOR l8 Sheets-Sheet 13 Filed Feb. 1. 1950 INVENTOR l B. ANDERSON A 7' TORNE Y F. B. ANDERSON 2,633,534

March 31, 1953 VARIABLE FREQUENCY OSCILLATOR 18 Sheets-Sheet 14 Filed Feb. 1, 1950 20 CPS SETTING IOKCSETT/NG -20db 411v u 7 F/G.238 Q I I I E ao/ a/ //o lgo/kc 3M6 SETTING.

I I I I I I I I I 00/'0//l 10 /00 m: /0 mo /Mc\/a loom 204/, K6

' l INVENTOR l: 8. ANDERSON 19%. (BMW ATTORNEY March 31, 1953 F. B. ANDERSON 2,633,534

VARIABLE FREQUENCY OSCILLATOR Filed Feb. 1, 1950 18 Sheets-Sheet 15 FIG. 24B Cb INDUCTIVE- I CONDENSER a l a Rb,

FIG. 240

f HIGH FREQUENCY l I 49, P0r.2 P02! FIG. 25 q BMW/ON DEV/ATION 0F P01 SETTINGS /N 1/5 N 7'01? 5 a. ANDERSON March 31, 1953 F. B. ANDERSON VARIABLE FREQUENCY OSCILLATOR F 18 Sheets-Sheet l6 iled Feb. 1, 1950 tz gL is ourpur EQUAL lZ/NG IMPEDANCE (/F DES/RED) VOLTAGE 0/v THERM/STOR DC OR AC ALONE (UNB/ASED) A C VOLTAGE ACROSS 7' HERM/S TOP 7] AND SERIES RES/$7I4NCE R WI 7' H D C BIAS cuma/vr THRU THERM/STOP DCB/AS l (DCB/AS THRU R7- //vv/v TOR E RANDERSON A r TORNE v 18 Sheets-Sheet 17 FREQUENCY CONTROL VOLTAGE F. B. ANDERSON VARIABLE FREQUENCY OSCILLATOR r4151 vr HAVING rRAlvsco/voucrxilvces 2 -Z8 DIFFERERE/VT av LOW IMPEDANCE CATHODENEI'WORK HIGH IMPEDANCE CATHODE NB'WORK //(c IOKC FIG. 2.9/1

IOOCPS IOCPS March 31, 1953 Filed Feb. 1, 1950 RCENT OFSET msous/vc (ZQEOUENCYCHANGE FOR INTERCHANGEOF V CONI'ROL VOLTAGE ATTORNEY FREQUENCY INVENTOR 8. ANDERSON March 31, 1953 F. B. ANDERSON VARIABLE FREQUENCY OSCILLATOR 18 Sheets-Sheet 18 Filed Feb. 1, 1950 FIG. 30

OUTPUT PHA$E4 o ourpur PHASE/ ourpur PHASE 2 OUTPUT FIG. 3/

' INVENTOR E B. ANDERSON mg W A TTORNEY Patented Mar. 31, 1953 VARIABLE FREQUENCY OSCILLATOR Frithioi"v B. Anderson,.Fanwood, N. J., assignor to BellTelephone Laboratories, Incorporated, New York, N. Y., .a corporation of New York App'lication'February 1, 1950, SeriaI'No. 141,621

11 Claims. 1

This invention relates to oscillation producing apparatus, and particularly to variable. oradjustable frequency bridge-type oscillation generators which may be adjusted over a wide orvery wide range of frequency values with relatively simple forms of frequency control, and which may be utilized, for example, in gain and phase measuring systems, in frequency modulating systems and in other variable frequency oscillation systems, and also in tunable amplifiers, as in amplifiers'for detectors, for example.

One of the objects of this invention is toprovide oscillation producing apparatus which may be operated over a wide or an extremely wide range of frequency values that, in extremecases, may be a frequency band ratio up to one billion to one, or more.

Another object of this invention is to provide variable frequency oscillation producing apparatus which may be continuously adjusted in frequency to any value within or over a wide range of frequency values, in one sweep of. a single. or other relatively simple form of frequency control means.

Another object of this invention is. toprovide considerable simplification in the control and other circuit components of wideerange. variable frequency oscillation producing apparatus.

Another object of this invention is to provide oscillation producing apparatus whichmay have a plurality of output circuits available in. a plurality of different phases.

Another object of this invention. is to improve the frequency stability and the. amplitude stability of variable frequency oscillation producing apparatus.

It is often desirable to be .able to realize in practical oscillators a continuous frequency sweep over a wide or very wide range of frequency values. In simple forms of oscillators" of known prior art types, the frequency band continuously tunable over any one range is usually quite limited to a comparatively narrow range. of :frequency values. Thus, in known oscillators of. the type having a simple tuning circuit'utilizing. a fixed inductance element and one 'ormorervariable capacitance elements, frequency bandsof. the order of about 3 to 1 are availablewhen utilizing a capacitance variation of theorder of aboutQ' to 1 in the capacitance tuning element thereof; and somewhat wider frequency ranges are availablein known oscillators of that type when utilizing therein a variable inductor type of tuningadjustment. Still wider frequency bands, up to the order of perhaps 1000 to 1, are available in known oscillators utilizing variations variable resistance and variable capacitancetuning' elements employed as components in Wien type bridges and other known types :of bridge configurations. Also, while very much wider frequency bands .of the order of up to around 1,000,000 to 1, or more, are available in known types of heterodyne oscillators, these are subject to certain disadvantages in that the output frequency at the low frequency end of the-fre quency range thereof particularly, depending as itv does on a relatively small frequency difierence between two relatively large frequency quantities, often results in comparatively poor frequency stability. Moreover, elaborate precautions are often required in order to prevent the two beating oscillators thereof from locking-into frequency step, and also additional measuresare often required to suppress undesired spurious or image responses that tend to occur in known types of the heterodyne oscillator.

In accordance with this invention, a variable frequency oscillation generator of the bridge type may be provided which may be operated overa wide or very wide range of variable frequency values comparable with, and even wider than, that obtainable in practice from the known heterodyne types of oscillator, but which at the same time avoids certain disadvantages peculiar to the heterodyne type of oscillator, and which results in improved performance and also considerable simplification in construction.

The variable frequency oscillation generator provided in accordance with this inventionmay comprise a feedback transmission loop circuit which may include therein either a single frequency-determining bridge, or two such frequency-determining bridges, provided with suitable associated sources of gain and connected in tandem circuit relation in the transmission loop circuit. With the use of two of such bridges in the circuit, a considerable amount of widening in the range of sweep frequency values may be obtained. The sources of gain that are associated with the bridge or bridges may comprise conventional vacuum type amplifier tubes, or other suitable sources of gain, which. are capable of providing a suitable amount of gain inthe transof I variablefrequency values-.obtainable, but-also 3 of the selection of any one of the adjustable frequency values available within the range of variable frequency values. Also, the bridges, due to their transmission characteristics, may exhibit a certain amount of amplitude control of the variable frequency oscillations in the circuit by maintaining a substantially or roughly constant or other desired transmission voltage ratio through the bridges and the remainder of the transmission loop, at all of such adjustable frequency value settings within the range of the available variable frequency values.

Also, in accordance with this invention, each of the adjustable bridges provided in the transmission loop circuit may have an output-toinput transmission or voltage ratio which, over the zero to infinity frequency band, is characterized by a phase shift varying substantially from to 180 degrees, namely, from 0 to 180 degrees in the first bridge, and from 180 to 0 degrees in the second bridge when used, so that in combination with incidental or other phase shifts contributed in other parts of the feedback transmission loop circuit, a resultant net phase shift of zero degree may be realized around the loop circuit with a gain of unity or more at any one of the oscillation frequency values within the range of variable frequency values provided by the bridges. The frequency of oscillation within the range of available frequency values, occurs at a substantially 90-degree phase shift position in one bridge, and at a substantially Z'ZG-degreephase shift position in the other bridge. If one bridge only is used, the remainder of the transmission loop furnishes the required phase shift. The contributions of the transmission loop, especially near the ends of the variable frequency range, will tend to shift the bridge phase shift contribution away from the 90-degree or Z'YO-degree positions. Both bridges may furnish phase shifts of 0 degree to 180 degrees or 180 degrees to 0 degree, or one alone may, and the required additional phase shift may be -made up in the remainder of the transmission loop.

' The bridge phase shifts may be adjusted over a wide range of frequency values by adjustment separately or simultaneously of the impedance value of one or more of the arms of either or of both of the bridges, as by means of a potentiometer arrangement, a signal responsive variable impedance electronic tube device, or by other suitable variable impedance means disposed on one or more arms of the bridge or bridges.

In a particular embodiment, the feedback 1' transmission loop circuit may include therein two --essentially similar frequency-determining bridge the bridge arms may have reactance character- 'istics that correspond to the range of the variable oscillation frequency values desired and that also may be capable of maintaining the amplitude level of such oscillations at a roughly constant or other predetermined value over the range of such variable oscillation frequency values, and

that will provide a phase shift substantially of 180 degrees for each of the two bridges. The

reactance networks referred to may be included in either a single series arm or in a single shunt networks utilized in the two bridges.

arm, or may be included in two adjacent arms comprising a series and a shunt arm of each of the two bridges.

In a more particular embodiment, the reactance networks may be two quite similar networks comprising one series arm of each of the two bridges, and the remaining three arms of each of the two bridges may comprise resistance or other type impedance arms. One or more of the bridge arms, such as the resistance arms thereof, may be varied in impedance value or in impedance ratio by any suitable frequency control means such as by a potentiometer arrangement to thereby adjust the value of the variable oscillation frequency values to any one of the such values within the range of frequency values provided by the reactance characteristics of the networks of the two bridges.

The reactance networks provided in the bridge arms may each comprise any suitable series and parallel combinations of impedance elements such as resistance and reactance elements of values suitable for covering the range of variable frequency values desired to be covered and utilized. The reactance elements of the networks may comprise capacitance type elements or inductance type elements or both, and may be of the lumped reactance type for use in the low and intermediate frequency ranges, or of the known tuned or resonant coaxial or other transmission line type for use in the higher frequency ranges.

In a particular embodiment, the reactance networks utilized in the bridge arms may comprise a plurality of series-connected sections of reactance and resistance elements, the reactance elements of the sections being capacitance or inductance elements, and the number of seriesconnected sections being in accordance with the range desired for the range of the variable frequency values in the particular circuit. Bridges employing such network combinations of reactance and resistance elements may be designed to provide a roughly constant or other predetermined transmission of energy at all of the desired frequency settings over a wide range of frequency adjustment, which may be in extreme cases up to the order of a frequency band ratio of 1,000,000,000 to 1, or more.

In a more particular embodiment, the networks utilized in the bridge arms may comprise,

as an illustrative example, a plurality of seriesconnected sections of parallel-connected resistance and capacitance elements, the number of such sections being two or more, as from two to ten or more such series-connected sections,

according to the extent of the range of variable frequency values desired for the particular circuit, it being understood that as the number of such series-connected RC' sections is increased, the range or number of octaves or decades of frequency values covered by the network is increased. Two similar bridges employing such RC networks utilizing such combinations of capacitance and resistance elements, may be readily designed to provide ranges of variable frequency values of the order of 100,000 to 1, and ranges up to 1,000,000,000, or more, to 1 may be realized, in extreme cases, by increasing the number of the reactance-resistance sections of the In the latter case, the range of variable frequency values might be, for example, values varying roughly from 0.01 cycle per second to 10 megacycles per second. 

